This invention relates to an electronic musical instrument of a type which controls tone characteristics such as tone volume by detecting touch data from a hammer interlocked with a key and, more particularly, to a technique for realizing optimum sounding of a tone which is generated based on bounding of the hammer.
Known is the art of an electronic musical instrument capable of producing a tone resembling a piano tone is the provision of a keyboard having hammers interlocked with keys for obtaining key touch feeling resembling one obtained in playing the piano (e.g., Japanese Patent Application Laid-open No. 91694-1988).
FIG. 5 shows an example of such prior art keyboard having hammers. In this figure, the structure of only one key, is shown in section. A column-shaped key support member KS is provided in a frame 10 and a key 12 is pivotably supported on this key support member KS. A column-shaped hammer support member HS is also provided in the frame 10 and a hammer 14 is pivotably supported on this hammer support member HS under the key 12.
The hammer 14 is provided with a projection EM which engages in an engaging recess ER formed in the side portion of the key 12. The hammer 14 is normally urged by a leaf spring 16 provided in the frame 10 to rotate upwardly about the hammer support member HS. The key 12 therefore is also urged to rotate upwardly through the projection EM of the hammer 14. The key 12 is provided in the end portion opposite to the portion supported by the key support member KS with engaging portions EPa and EPb. The engaging portion EPa can engage with a stop SP provided on the frame 10 from below and thereby determine the key releasing position by restricting the upward rotation of the key 12. The engaging portion EPb can engage the stop SP from above and thereby determine the deepest depressed position of the key 12 restricting the downward rotation of the key 12.
A plate PL is provided on the frame 10 at a position below the hammer 14. Switches MK1 and MK2 are provided in parallel to each other on the plate PL. The hammer 14 is provided at positions corresponding to the switches MK1 and MK2 with projections P1 and P2 for actuating the switches MK1 and MK2. The length of the downwardly projecting portion of the projection P1 is so set that it is longer than that of the projection P2. For this reason, when the hammer 14 has been moved downwardly in an interlocking motion with depression of the key 12, the switch MK1 is first turned on by the projection P1 and then the switch MK2 is turned on by the projection P2: In this case, time between start of turning on of the switch MK1 and start of turning on of the switch MK2 is shorter if the speed of depression of the key 12 is faster. Therefore, by controlling tone characteristics such as tone volume by detecting this time, a tone can be generated in accordance with the strength of key touch.
For restricting the downward rotation of the hammer 14, a damper DP is provided on the frame 10. The upward rotation of the hammer 14 is restricted by the key 12. When the key 12 is depressed slowly, bounding of the hammer 14 hardly occurs but when the key 12 is struck strongly, bounding of the hammer 14 often occurs. More specifically, the hammer 14 is depressed with depression of the key 12 and then displaced upwardly in reaction upon striking against the damper DP independently of the key 12 before the key 12 is released, and then displaced downwardly in reaction upon striking against the key 12. Such upward and downward bounds sometimes are repeated several times.
FIG. 6 is a graph showing an example of the conventional key-on touch detection and particularly such detection when the hammer bound has occurred.
When the key 12 is depressed to the deepest depression level L2 from level L1 in a key release state, the key 12 will follow the path as shown by curve A whereas the hammer 14 will follow the path as shown by curve B if the hammer bound occurs. The switch MK1 therefore is turned on at time t1 and turned off at time t4 and then is turned on again at time t5 so that an on-off signal C is obtained from the switch MK1. The switch MK2 is turned on at time t2 and turned off at time t3 and then is turned on again at time t6 so that an on-off signal D is obtained from the switch MK2.
In controlling tone generation in response to the signals C and D, first key-on data is generated at time t2 at which the switches MK1 and MK2 are both turned on, first key-off data is generated at time t4 at which the switches MK1 and MK2 are both turned off and second on data is generated at time t6 at which the switches MK1 and MK2 are both turned on again. Further, length of time between time t1 at which the on state of the switch MK1 is started and time t2 at which the on state of the switch MK2 is started is counted and first touch data TD1 corresponding to this time length is generated. Also, length of time between time t5 at which the on state of the switch MK1 is started again and time t6 at which the on state of the switch MK2 is started again is counted and second touch data TD2 corresponding to this time length is generated.
FIG. 7 shows a tone envelope shape produced on the basis of the above described key-on data, key-off data and touch data. The first tone is generated at time t2 in response to the first key-on data and starts to decay at time t4. The touch volume of the first tone is controlled in response to the first touch data TD1 but does not reach the peak level Lp corresponding to the touch data TD1 because the tone volume starts to decay at time t4 in response to the key-off data, so that the amplitude envelope assumes a shape as shown by curves A1 and A2.
Then, the second tone is generated at time t6 in response to the second key-on data. In response to generation of second key-off data at time tR upon release of the key 12, the second tone starts to decay. At this time, the tone volume of the second tone is controlled in response to the second touch data TD2 but, since the touch data TD2 corresponds to a tone volume level lower than the touch data TD1 (time length between time t5 and time t6 is longer than time length between time t1 and time t2), the amplitude envelope assumes a shape as shown by curves B1 and B2. The second tone normally predominates in the hearing sense so that it is difficult for a listener to discriminate the first tone from the second tone.
When a key has been struck strongly, it is desirable that an envelope amplitude as shown by the curves A1, A3 and A4 be obtained. In the prior art device, however, the tone volume of the second tone is controlled in response to the touch data based on a hammer bound and, accordingly, the amplitude envelope assumes a shape as shown by the curves B1 and B2. That is to say, such a tone is obtained is that could be obtained if the key was struck weakly in spite of the fact that the key has actually been struck strongly, with the result that discrepancy arises between the key touch feeling and the actually obtained tone.
For coping with this problem, it is conceivable to prohibit a tone control based on key-off data and key-on data within a predetermined length of time To starting from a time point immediately after time t2 and including times t4 to t6. According to this method, however, when a key is depressed weakly and released within the time To, decay of the tone is delayed from release of the key and starts from the end point of the time To, with the result that discrepancy arises between the feeling of the key release and the actually obtained tone.